CVE-2026-45364
Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
- State
- Published
- Severity
- 7.3 High
- Published
- May 28, 2026
- Updated
- May 29, 2026
- Reserved
- May 12, 2026
Description
Better Auth is an authentication and authorization library for TypeScript. Prior to 1.4.17 and 1.5.0-beta.9, Better Auth's HTTP rate limiter keyed each request by the exact textual IP address it received in x-forwarded-for (or the configured IP-bearing header). IPv6 clients controlling a typical /64 allocation could rotate through 2^64 distinct source addresses without exhausting the per-address counter, defeating rate limiting on /sign-in/email, /sign-up/email, /forget-password, and every other path the limiter protects. The same bug allowed a single client to vary the textual encoding of one IPv6 address (uppercase, compression, IPv4-mapped, hex-encoded IPv4-in-IPv6) and produce multiple distinct keys. This vulnerability is fixed in 1.4.17 and 1.5.0-beta.9.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 7.3 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L | GitHub_M |
Weaknesses
- CWE-307 Improper Restriction of Excessive Authentication Attempts
Affected Products
| Product | Versions |
|---|---|
better-authbetter-auth |
|
References
- https://github.com/better-auth/better-auth/security/advisories/GHSA-p6v2-xcpg-h6xw
- https://github.com/better-auth/better-auth/pull/7470
- https://github.com/better-auth/better-auth/pull/7509
- https://github.com/better-auth/better-auth/commit/43e719bcc0c223c7079fa0c611a9cf7ea1188254
- https://github.com/better-auth/better-auth/commit/57af0f7b910dcf7b1a5c0615d10b9bd56bb69bef
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